The GNU Lesser General Public License (formerly the GNU Library General Public License) is an FSF approved Free Software license designed as a compromise between the GNU General Public License and simple permissive licenses such as the BSD license and the MIT License. It was written in 1991 (and updated in 1999) by Richard Stallman and Eben Moglen.

The main difference between the GPL and the LGPL is that the latter can be linked to a non-(L)GPLed program, which may be free software or proprietary.

The LGPL places copyleft restrictions on the program itself but does not apply these restrictions to other software that merely links with the program. There are, however, certain other restrictions on this software. Essentially, it must be possible for the software to be linked with a newer version of the LGPL-covered program. The most commonly used method for doing so is to use "a suitable shared library mechanism for linking". Alternatively, static linking is allowed if either source code or linkable object files are provided.

The LGPL is primarily intended for software libraries, although it is also used by applications such as OpenOffice.org and Mozilla.

One feature of the LGPL is that one can convert any LGPLed piece of software into a GPLed piece of software (section 3 of the license). This feature is useful if one wants to create a version of the code that software companies cannot use in proprietary software products. It is also necessary to ensure that the LGPL is "GPL-compatible", so that GPL-covered programs can use LGPL-covered libraries.

The LGPL is now deprecated by the FSF, on the grounds that a GPLed library forces the software using it to be under the GPL also, and hence creates more free software.

See also

• List of programs released under the GPL
• BSD and GPL licensing
• GNU Free Documentation License
• GNU General Public License
• GNAT Modified General Public License

External links

• Text of the new "Lesser" GPL
• Text of the old "Library" GPL
• "Why you shouldn't use the Library GPL for your next library" by Richard Stallman